<template>
  <ul class="list">
    <li class="item"
        v-for="(item,index) of letters"
        :key="item"
        @click="handleLetterClick"
        @touchstart="handTouchStart"
        @touchmove="handTouchMove"
        @touchend="handTouchEnd"
        :ref="item"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
  export default {
    name: "CityAlphabet",
    props: {
      cities: Object
    },
    data: function () {
      return {
        touchStatus: false,
        startY : 0,
        timer:null,
      }
    },
    updated:function(){
      this.startY = this.$refs['A'][0].offsetTop
    },
    computed: {
// 计算属性
      letters: function () {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    methods: {
      handleLetterClick: function (e) {
        this.$emit('change', e.target.innerText)
      },
      handTouchStart: function () {
        this.touchStatus = true
      },
      handTouchMove: function (e) {
        if (this.touchStatus === true) {
          if(this.timer){ clearTimeout(this.timer) }
          this.timer = setTimeout(() =>{
            const touchY = e.touches[0].clientY
            const index = Math.floor((touchY - this.startY)/21)-5
            if(index >= 0 && index < this.letters.length){
              this.$emit('change',this.letters[index])
            }
          },16)
        }
      },
      handTouchEnd: function () {
        this.touchStatus = false
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~@/assets/styles/varibles.styl"
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.78rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .44rem
      text-align: center
      color: $bgColor
</style>
